Refrigeration defrost control responsive to operation of compartment air circulating fan



April 8, 1969 P. F. HARBOUR 3, ,9 9

REFRIGERATION DEFROST CONTROL RESPONSIVE TO OPERATION OF COMPARTMENT AIRCIRCULATING FAN Filed Sept. 29, 1967 34 I A.C. L 36\ DEFROST HEATERflUUULflILIV DEFROST COMPARTMENT THERMQSTAT THERMOSTAT F 1 DRAIN HEATERvi EVAPORATOR /38 Li I n REFR.DEFROST 3O CONTROL SW.

lo COMPRESSOR l MOTOR PROTECTOR I CONDgNSER CONDENSER FAN WlTNESSESIINVENTOR M Philip E Harbour ATTORNEY United States Patent 3,436,929REFRIGERATION DEFROST CONTROL RESPON- SIVE TO OPERATION OF COMPARTMENTAIR CIRCULATING FAN Philip F. Harbour, Columbus, Ohio, assignor toWestinghouse Electric Corporation, Pittsburgh, Pa., a corporation ofPennsylvania Filed Sept. 29, 1967, Ser. No. 671,686 Int. Cl. F25d 21/06;G05d 23/32 US. Cl. 62155 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUNDOF THE INVENTION Field of the invention.

The invention pertains to the art of controlling refrigeration devices.

Description of the prior art It has been heretofore proposed toeliminate the usual separate timer motor used to control switch meansfor periodically effecting defrost of the refrigerator evaporator byinstead driving the refrigeration-defrost control switch means directlyfrom the motor driving the fan which circulates air over the evaporatorand through the refrigerated compartment. One published example of suchan arrangement is found in US. Patent 3,159,980 in which the duration ofthe defrost cycle is controlled by a dashpot arrangement so that arefrigeration cycle is not again initiated until the dashpot controlledtime has expired. This dashpot technique has the inherent advantage ofpermitting the duration of the defrost cycle to be set in excess of theactual time required for completing the defrost of the evaporator. Thisallows the evaporator to cool somewhat before the compressor andcompartment fan are again energized, and accordingly reduces the loadupon the compressor when it again starts. This overage of time for adefrost cycle is conventional also in those arrangements in which aseparate timer motor is used to control the defrost period, since thetimer is typically set to allow a period of, say, 2 5 minutes fordefrost, while the evaporator is typically defrosted in, say, 10minutes. While as noted the dashpot arrangement does have the inherentadvantage of permitting the setting of a duration of refrigerationsystem dormancy to exceed the actual time required for defrost, thedashpot arrangement may be considered to constitute a timer of sortsitself so that in effect one timer (the dashpot) has been substitutedfor another.

SUMMARY OF THE INVENTION It is proposed in accordance with the presentinvention that the restoration of the refrigeration-defrost controlswitch means to a refrigeration position be effected by a circuitarrangement and swtiching means devoid of a dashpot timer, and as soonas the evaporator has been defrosted. The circuit is also arranged topermit the early resumption of compressor operation for refrigerationpurposes without imposing such a load upon the compressor that overloadtripping occurs.

In brief, the invention provides that the compartment fan motor (whichdrives the refrigeration-defrost control switch between its alternaterefrigeration and defrost positions at the expiration of selectedaccumulated times of fan motor operation), and the compressor motor, beshunted by a defrost thermostat during the defrost operation to preventthe energization of the compartment fan motor and compressor motor.Completion of defrost opens the defrost thermostat to momentarilyenergize the compartment fan motor through a completed circuit whichincludes the defrost heater, the fan motor and the compressor motor, toshift the control switch back to a refrigeration position. The highimpedance of the compartment fan motor relative to the compressor motorprecludes any attempt of the compressor motor to start while theshifting of the switch takes place. Restoration of the control switch tothe refrigeration position deenergizes the compartment fan motor andenergizes the compressor motor. After the compressor operation haspulled down the temperature of the evaporator to a level which causesthe defrost thermostat to close, the compartment fan is again energized.

In the preferred embodiment of the invention, which is particularlyadaptable to larger size refrigerators, the condenser fan is connectedin the circuit arrangement so that it operates independently of therefrigeration-defrost control switch position. The result of thisarrangement is that the condenser fan circulates air over the condenserduring the defrost operation, and also over the compressor, so thatlower condenser temperatures and lower compressor motor windingtemperatures exist at restart. The lower condensing temperature promotesmore rapid condensation of gas in the high side and therefore reducesthe load against which the compressor must work. Of course the lowerwinding temperatures in the compressor motor also means lower windingresistance allowing the compressor motor to produce a higher startingtorque.

DRAWING DESCRIPTION The single figure is an electrical schematic anddiagrammatic representation of a refrigerator incorporating a circuitarrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing, the broken lineoutline 10 represents the storage compartment of the refrigeratingdevice (hereinafter called the refrigerator), which may be a typicaldomestic refrigerator or freezer.

The refrigeration system includes the usual refrigeration componentssuch as the refrigerant compressor 12 driven by motor 14, refrigerantcondenser 16, and refrigerant evaporator 18. The refrigerant conductingconduits connecting the refrigerant components are omitted for clarity.Also, the drawing does not illustrate the specific locationalrelationships between the parts of the refrigeration system, although itis noted that the evaporator will conventionally be located in apassageway separate from the interior of the storage compartment 10 withthe compartment fan 20 located to direct a draft of air through thepassageway, the compartment and back into the passageway. The compressor12 and its motor 14, along with the condenser 16 are conventionallylocated in the machine compartment of the refrigerator outside of thegeneral confines of the storage compartment 10. These latter elementsare physically located so that the condenser fan 22 creates a draft ofair through the condenser and over the compressor and motor casing. Thegeneral direction of air flow created by the two fans 20 and 22 isindicated by the broken line arrows associated therewith.

The defrost heater 24 is disposed in heat exchange re lation with theevaporator 18 in the noted separate passageway to effect its defrost.The defrost thermostat 26 is located so as to be responsive to thetemperature condition of the evaporator. The defrost thermostat has anormally closed position in response to a temperature indicating anormal refrigerated condition of the refrigerator. Upon detecting adefrosted condition of the evaporator, the thermostat opens.

Among the other main components of the arrangement of concern inconnection with the invention are the refrigeration-defrost controlswitch 28 which has a refrigeration position (solid line) and analternate defrost position (broken line) to which it is periodicallymoved through a gear system after a predetermined accumulated runningtime of the compartment fan motor 30. The period of time during onerepeating cycle of fan motor operation that the switch 28 is in adefrost position is very minute compared to the period during which theswitch is in a refrigeration position; it only being necessary that theswitch does not move through the defrost position and back to arefrigeration cycle while the fan motor coasts to a stop. The storagecompartment is provided with a compartment thermostat 32 which, undernormal conditions, initiates and terminates the operation of therefrigeration system in accordance with variations in the compartmenttemperature above and below, respectively, the set point to which thethermostat is adjusted. The opposite sides of the electrical powersource are identified as 34 and 36.

Operation Under normal refrigerating operation of the system, thecompartment thermostat 32 closes in response to a compartmenttemperature calling for cooling. This completes a refrigerationproducing circuit from the thermostat 32 through line 38, switch 28 inits refrigeration position, line 40 connecting one side of thecompressor motor 14 to the switch 28, and line 42 connecting the otherside of the compressor motor through a thermal overload motor protector44 to the opposite line 36 of the power source. The compartment fanmotor 30 is also energized at this time through the control switch 28 inits refrigeration position, line 40 connected to one side of the fanmotor, and line 46 connecting the other side of the fan motor to thedefrost circuit between the defrost heater 24 and the defrost thermostat26. It will be appreciated that the defrost thermostat 26 is in anormally closed position due to the undefrosted condition of theevaporator 18. The condenser fan motor 48 is also energized when thecompartment thermostat 32 closes since line 38 is con nected to one sideof the motor, and the other side of the motor is connected to the powerline 36.

After the compartment fan motor 30 has accumulated a predeterminedamount of running time (corresponding to an expected defrost need), thecontrol switch 28 is driven by the motor rotation from its refrigerationposition to its alternate defrost position. The defrost circuit willthen be energized through the control switch 28 in its defrost position,line 50 connecting the switch 28 to the defrost heater 24, and line 46connecting the defrost heater to the one side of the closed defrostthermostat 26. When the switch 28 is moved to its defrost position, thecompartment fan motor 30 and the compressor motor 14 are deenergized byloss of their direct connection through switch 28 and by being shuntedby closed defrost thermostat 26 with respect to their connection throughline 46 and the defrost heater.

After sufficient heat has been generated by the energized defrost heater24 to defrost the evaporator 18, the defrost thermostat 26 opens.Removal of the shunt circuit across the compartment fan motor 30 andcompressor 12 by opening of the defrost thermostat 26 results in theenergization of the fan motor 30 through a completed circuit includingthe control switch 28 in the defrost position, line 50, defrost heater24, line 46, the compartment fan motor 30, line 40, compressor motor 14,line 42, and motor protector 44 to the power line 36. However the fanmotor energization is only momentary since the motor operation shiftsthe control switch 28 back to its illustrated solid line refrigerationposition. The impedance relationship between the defrost heater 24,compartment fan motor 30, and the compressor motor 14 precludes thecompressor motor from attempting to start during this momentaryenergization of the fan motor. The compartment fan motor 30 has arelatively high impedance (e.g., 300 ohms) as compared to the defrostheater (e.g., 35 ohms) and compressor motor (e.g., 8 ohms) so that thevoltage drop produced across the compartment fan motor is adequate toenergize it, but the drop across the compressor motor is negligible.With control switch 28 back in its refrigeration position, thecompartment fan motor 30 is deenergized and the compressor motor 14 isenergized. Until the evaporator is adequately chilled by compressoroperation, the defrost thermostat 26 remains open and the compartmentfan motor does not operate. This avoids forcing warm air into thestorage compartment. Then when the defrost thermostat closes, thecompartment fan operates again in its usual way under the control of thecompartment thermostatv As noted before, in the preferred embodiment thecom denser fan motor 48 is energized during the defrost cycle tocirculate air through the condenser 16 during the defrost period andover the compressor 12 and compressor motor 14. Thus, when thecompressor is energized after the defrost, the load against which thecompressor must work is reduced as compared to the load against it whichwould work if the condenser fan were not operating during defrost.

It is noted that in certain instances, where the refrigerating system ismore than marginally sized for the potential load, the one side of thecondenser fan motor 48 may be connected to line 40 rather than directlyto line 38 so that it does not run during the defrost operation.However, in either case it will be appreciated that the circuitarrangement is such that the refrigeration-defrost control switch isdirectly driven from the compartment fan motor, thereby avoiding anyrequirement of a substitute timing element in place of a separate timingmotor as has normally been conventional.

I claim as my invention:

1. In a refrigerated storage device of the type in which the fan motorfor circulating air through the storage compartment and evaporator movesa two position switch from a refrigerating position to a defrostposition in accordance with accumulated running time of said motor, acircuit arrangement between one side of a compartment temperatureresponsive switch and one side of a power source comprising:

a defrost effecting circuit including, in series, said two positionswitch in a defrost position, a defrost heater, and a defrost thermostathaving a closed position in response to normal evaporator temperaturesand operable to an open position in response to a defrosted condition ofsaid evaporator;

a refrigeration effecting circuit including, in series, said twoposition switch in a refrigeration position and a refrigerant compressormotor;

a circulating fan motor circuit connecting one side of said fan motor tosaid defrost effecting circuit between said defrost heater and defrostthermostat, and the other side of said fan motor to said refrigerationeffecting circuit between said two position switch and said compressormotor;

whereby said circulating fan motor, in shunt with said defrostthermostat during a defrost operation, is prevented from being energizeduntil said defrost thermostat opens, and is then energized momentarilythrough a series circuit including said two position switch in saiddefrost position, said defrost heater and said compressor motor to movesaid two position switch back to said refrigeration position.

2. A circuit arrangement according to claim 1 wherein: said circulatingfan motor and said defrost heater together have a high impedancerelative to said compressor motor so that the voltage drop across saidcompressor motor during said momentary energization of said circulatingfan motor is sufficiently low that said compressor motor does notattempt to start.

3. In a refrigerated storage device having a circuit arrangementaccording to claim 1:

a condenser fan circuit including a condenser fan motor having one sideconnected to said compartment temperature responsive switch and itsother side connected to said one side of said power source so that saidcondenser fan motor is energized independently of said two positionswitch position, and thereby operates during defrosting of saidevaporator.

4. In a refrigeration device:

a refrigerated compartment;

a refrigeration system including compressor means, condenser andevaporator;

compartment fan means for creating a flow of air over said evaporatorand compartment;

condenser fan means for creating a flow of air over said condenser andsaid compressor;

a compartment thermostat;

a refrigeration-defrost control switch driven to alternate refrigerationand defrost positions by accumulated running time of said compartmentfan means;

a defrost heater associated with said evaporator;

a defrost thermostat having a normally closed position in response to achilled position of said evaporator and operable to an open position inresponse to a defrosted condition thereof;

an electrical power source;

a compressor circuit connecting said compressor means to said controlswitch for energization when said control switch is in saidrefrigeration position;

a defrost circuit connecting said defrost heater and defrost thermostatin series to said control switch for energization of said defrost heaterwhen said control switch is operated to said defrost position, saiddefrost circuit being opened by said defrost thermostat responding to adefrosted condition of said evaporator;

a compartment fan circuit connecting one side of said compartment fanmeans to said defrost circuit between said defrost heater and saiddefrost thermostat, and the other side of said compartment fan means tosaid compressor circuit between said control switch and said compressormeans;

whereby said defrost thermostat is in shunt with said compartment fanmeans and compressor means during defrost to prevent their operationand, upon said defrost thermostat opening in response to a defrostedcondition of said evaporator said compartment fan means is energizedthrough said defrost heater to move said control switch back to saidrefrigeration position.

5. In a refrigeration device according to claim 4:

said compartment fan means has a high impedance relative to saidcompressor means so that the voltage drop across said compressor meanswhen said defrost thermostat opens is sufficiently small that saidcompressor means does not attempt to start.

6. In a refrigeration device according to claim 4 including:

UNITED STATES PATENTS 2,662,380 12/1953 Sutton 62-455 3,029,611 4/1962Kuhn 62155 3,063,250 11/1962 Moorman 62155 MEYER PERLIN, PrimaryExaminer.

US. Cl. X.R.

